The treaty’s architects hoped that, over time, nations would strengthen their climate pledges as momentum for action grew. Ahead of Glasgow, the United Nations asked for a fresh round of more ambitious national plans that stretch out to at least 2030.

Some countries have offered to do more. President Biden, for instance, pledged that the United States would cut its greenhouse gas emissions 50 percent below 2005 levels by 2030, roughly double its previous goal. Britain, Canada, Japan and the European Union have also vowed to cut emissions more deeply over this decade.

But other major emitters, including India, Turkey and Saudi Arabia have not submitted new short-term pledges as of yet. And the report found that some of the updated pledges, such as those from Russia or Australia, were unlikely to lead to any actual emissions reductions between now and 2030.

China, the world’s largest emitter of greenhouse gases, remains a wild card. Although the country has not yet officially updated its Paris agreement pledge, President Xi Jinping has said that China’s emissions could peak before its previous target of 2030, while the country plans to accelerate its development of renewable and nuclear power.

If those targets are met, the U.N. report found, that could nudge down expected future emissions further, though the world would remain sharply off track from its Paris agreement goals. Environmentalists have called on China to do far more to rein in its appetite for coal, the dirtiest of all fossil fuels.

The new report also warns that even these new climate pledges are only as good as the policies that back them up. That is still a major question mark.

The European Union, for instance, has proposed sweeping new climate legislation — including stricter caps on industrial emissions, new targets for electric vehicles and a border tax on carbon-intensive imports — to achieve its goal of slashing emissions 55 percent below 1990 levels by 2030. But those proposals still need approval from all 27 member states, and many remain contentious with industry groups.

In the United States, the Biden administration is still struggling to clarify exactly how it will meet its pledge, since major climate legislation has not been approved by Congress. One recent analysis found that the country might be able to meet its target with a combination of generous tax incentives for wind, solar and other clean energy, tough regulations to restrict pollution from power plants and automobile tailpipes, and a slew of climate laws enacted by states. But none of those actions are yet assured.

On top of that, most countries have largely squandered the chance for a “green recovery” in the wake of the coronavirus pandemic, the report said. While governments spent more than $16 trillion on stimulus measures over the past year, they largely focused on reviving the traditional fossil-fuel dependent parts of their economies as quickly as possible, with less than one-fifth of recovery funds used to promote low-carbon alternatives. As a result, global emissions are expected to rebound sharply this year after declining in 2020.

The new U.N. report also noted that more than 50 countries have now adopted formal goals to reach “net zero” emissions, which is essentially a promise to stop adding greenhouse gases to the atmosphere by a certain date. The United States has vowed to get to net zero by 2050. China says it will aspire to do so by 2060. This week, Saudi Arabia unveiled a net zero goal.

In theory, those goals could have a powerful effect. The report estimates that if countries all followed through, the world could potentially limit global warming to around 2.2 degrees Celsius by 2100.